1. Field of the Invention
The present invention relates to a switching regulator having low power consumption and able to operate efficiently under low workload conditions.
2. Description of the Related Art
In the related art, it is well known that a switching regulator is set to operate in a PWM control mode under usual workload conditions, and is set to operate in a PFM control mode under low workload conditions.
In the PWM control mode, the switching regulator is set to operate at a fixed frequency, and an ON-duty in each cycle is modulated to adjust an output voltage. In the PFM control mode, the ON-duty in each cycle (the time interval in the ON state) is fixed, but the operating frequency is modulated to adjust the output voltage. In addition, there is a pseudo-PFM control mode, in which the ON timing is controlled at a fixed frequency, and the ON timing is skipped, thereby, realizing performance close to the PFM control mode.
For example, Japanese Patent Gazette No. 3647811 (hereinafter referred to as “reference 1”) discloses a DC-DC conversion circuit in which an output voltage of a converter is detected, and based on an error output voltage generated from a difference between a divisional voltage of the output voltage and a reference voltage from a reference voltage source, the driving mode of the converter is switched from the PWM mode to the pseudo PFM mode, or from the pseudo PFM mode to the PWM mode.
However, in the invention disclosed in reference 1, since the pseudo PFM mode is utilized, it is necessary that a circuit of large power consumption, such as an oscillation circuit for outputting the fixed frequency, be constantly in operation. In addition, in the pseudo PFM mode disclosed in reference 1, a ripple voltage occurs in the output voltage.